Magnetron output coupling system



1954 A. M. CLOGSTON ETAL 86 MAGNETRON OUTPUT COUPLING SYSTEM Filed June 21, 1946 7 FIGJ FIG-3 INVENTORS -CLOGSTON ALBERT M lTH ALEXANDER 6.5M

ATTORNEY Patented Jan. 19, 1954 Albertv M. Clogston, New York N. Y, and Alex ander, G.. Smith,v Durham. N.. 0., assignors, by mcsne assignments, to the, United States of, America as represented by the Secretary of War Application .Iune .2,t, 1946, Serial No. 678,240

1.0, Claims.v

This invention relates generally to magnetronoscillators, and, more particularly, to means for extracting oscillatory energy from. such devices.

In the generation of hyper-frequency: oscillat tions, the magnetron-type electron, discharge de-. vice. hasv proved exceptionally useful. This tube is capable of generating centimeter waves at. power levels of kilowatts. At the shorter of. the wavelengths which; are. in common use, it-ismost, convenient to employ wave guide. energy transmission systems in conjunction with. the ma netron oscillator in order to reduce power losses to a. However in the past, the mostreadily practicable means of coupling energy from a magnetron to a transmission system has been found to be a. section Oif coaxial line. the center conductor of which projects into. the mag:- netron shell in the formof a small, loop; or probe. It. can be, seen that. if such output coupling is. used, there must needs be another coupler be.- tween thecoaxial section and the wave: guide line. The disadvantagesof; this type of system are numerous. The losses introduced by the coaxial line are appreciablei. the; couplers: are not. 100 per cent eflicient and; the losses; therein are multiplied by the number of such coupling devices; and a coaxial; line is not capable of handling. asv high power; as is a wave g-uidahencea limitation is put; on the peak; power which the entire system can handle. Furthermore, at the shortest Wavelengths, the. extremely small size of the magnetron and energy carrying components renders: itv diflicult to fabricate a coaxial output.

Accordingly, it is. one object of the present in- 1 vention to provide means of couplingmagneb11011 oscillators directly to a wave guide transmission line, without; the. use. of coaxial components...

Another object is to. provide. a magnetron out.- put system. capable of handling high oscillatory power.

Stillanother object is to provide magnetron Output means which, may be conveniently manufactured regardless of the frequency for which it is designed.

Briefly, the invention is embodied in a magnetron oscillator having a longitudinal slot in its outer shell. To this slot is attached a wave guide section which changes from a width approximately that of the slot to the width of the main wave guide. Probes, loops, on coaxial com;- ponents are. not necessary.

The. principles and operation of our inventionwill be more apparent to those skilled in. the art. upon reference to. the following specification and claims; and to the drawings in which;

Fig. l is a. sectional plan view of: a magnetron and wave guide coupler constructed according, to the principles of my invention;

Big. 2 is a longitudinal section through. the. magnetron. and coupler of Fig. 1 along the. line 2-2, omitting the cathode; and

Fig. 3-. shows, another type of. coupler which. may be used.

Referring now to Fig. l, a horizontal. section through a vane-type magnetron. is: shown. lEThe principal components of this type, of. magnetron. are the. shell 5,, vanes 6-, and cathode l Vanes. 6. partition the, interior of the. shell into individual resonant. cavities. Electrons areemitted from cathode, 1 and describe. an orbital path about the cathode. As the electrons move past the entrance to each cavity, oscillations are. setv up, within. the cavity at. a trequency. chiefly de. termined by its physical dimensions. A relatively narrow slot 8 is cut. through wall 5. into one of these, cavities to allow egress of energy. Wave-v guide section It is attached to, the magnetron. by sealing its walls hermetically to magnetron shell 5. Since the-width. of. slot 8 is muchless. than that of the main wave. guide 9 thewalls. of guide section tfltaper smoothly to effect a. transition in dimensions; The taper also has the effect of matching the impedance of the-.oscillator tothat of. guide a as wil1; be; elaborated; hereinafter. A glass window ll is sealed into the guide. to allow evacuation of: the: magnetron tube. The precise location of. the window is not; critical. and itmay be placed at whatever point in the wave guide is most convenient.- for its in sertion Fig. 2 is alongitud-inal section through the. ap-- paratusof Big.. 1 along the 1ine-Z--2-. illustrating the height of slot 8 and the fact that. the. upper and lower Walls of guide Section N) are parallel.

In general. the output impedance ofthe, mag.- netron: will, not. be: the same. as the input; impedance. of the main. wave guide. hence there the problem of. matching these. two. impedances- It hasv been found that the ratio. of; the energy remaining within the magnetron anode to. that propagated down the wave: guide. is. substantially equal t the. ratio of theimpedanoe. of the anode to that of wave uided). during. each r. ole of oscillation. Experimentation. has shown that this ratio must; be maintained within certain limitsin. order that; the magnetron may act:

as an, eflicient generator of power. The-tapered transition. section provides a. gradual transfor mation; of impedances. since. the impedance.- of each incremental length of wave guide is: propor tional to the; width of the.- guide. The cut off wavelength of the. guide, being dependent only. on the.- longer cross-sectional dimension of the guide. (for the-most: commonly used- TEo;1 mode), is. unaffected.

However, a tapered section is not the only means of impedance transformation possible, an-

The quarter wavelength transformer is a means of impedance transformation well known in the art. It is particularly useful whenmatching between elements difiering widely in impedance,

In this case, it offers certain advantages in simplicity of construction over the tapered transition section shown in Figs..1 and 2. However both forms of impedance transformation devices have been found practicable. 7

While there has been described hereinabove what are at present considered to be preferred embodiments of the present invention, it will be obvious to those skilled in the art that changes and modifications may be made therein without exercise of inventive ingenuity. Hence, all such modifications and adaptations are claimed as may fall fairly within the true spirit and scope of the invention.

What is claimed is:

1. In a hyper-frequency energy generation system, a magnetron electron discharge device having a source of electrons, said device having a plurality of cavity resonators symmetrically disposed about an axis, a rectangular wave guide, a transitional section of wave guide of rectangular cross-section having one end connected to said rectangular wave guide and its other end abutted against the outer wall of said magnetron and hermetically sealed thereto, a substantially rectangular passage being provided in the mag netron wall opening into the interior of said transitional section and one of the cavity resonators of said magnetron, said passage extending axially substantially the height of said cavity resonator and said transitional wave guide section and being appreciably narrower in width than said cavity resonator, said transitional wave guide section having a constant height in the axial direction.

2. The invention in accordance with claim 1 wherein there is progressive variation in the width of said transitional wave guide section.

3. The invention in accordance with claim 1 wherein in addition said transitional wave guide section is in length substantially one-quarter of a wavelength of the oscillatory energy contained therein.

4. In a hyper-frequency energy generation system, a magnetron electron discharge device having a, source of electrons, said device having a plurality of cavity resonators symmetrically disposed about an axis, a rectangular wave guide, a transitional section of wave guide of rectangular cross-section having one end connected to said rectangular wave guide and its other end abutted against the outer wall of said magnetron and hermetically sealed thereto, said outer wall having an elongated passage opening into the interior of said transitional section and one of the cavity resonators of said magnetron, said passage extending axially substantially the height of said transitional wave guide section and being appreciably narrower in width than said one cavity resonator, said transitional wave guide section having a constant height in the axial direction equal to the longer cross-sectional dimension of the said rectangular wave guide and a constant width equal to the width of said passage, said transitional section being a quarter wavelength long at the operating frequency of the magnetron.

5. In a hyper-frequency energy generation system, a magnetron electron discharge device having a source of electrons, said device having a plurality of cavity resonators symmetrically disposed about an axis, a rectangular wave guide, atransitional'section of wave guide of rectangular cross-section having one end connected to said rectangular wave guide and its other end abutted against the outer wall of said magnetron and hermetically sealed thereto, said outer wall having a substantially rectangular aperture opening into the interior of said transitional sectionand one of the cavity resonators of said magnetron, said aperture extending axially substantially the height of said cavity resonator and said transitional wave guide section and being appreciably narrower in width than said one cavity resonator, said transitional wave guide section having a constant height in the axial direction equal to the longer cross-sectional dimension of said rectangular wave guide, and having a constant width substantially equal to that of the aperture, the length of said transitional section being a quarter wavelength at the operating frequency of the magnetron, the width of said transitional section being such that said transitional section matches the impedance of said cavity resonator to the impedance of said rectangular wave guide.

6. In combination, an evacuated magnetron having a source of electrons and a plurality of cavity resonators, an output circuit for said magnetron comprising an output rectangular wave guide having a constant height and a width that is smaller than its height, and an impedance matching transformer consisting of a wave guide having a rectangular cross-section and having a constant height and a width that is smaller than its height, said transformer wave guide being coupled at one end to a cavity resonator of said magnetron and at its other end to said output wave guide, the width of said transformer wave guide at at least one end thereof being less than the width of said output wave guide.

7. The combination of claim 6, further including a window sealing one of said wave guides to retain the vacuum of said magnetron, said window being transparent to the energy propagated along said guides.

8. The combination of claim 6, wherein said transformer wave guide is tapered.

9. The combination of claim 6, wherein said transformer wave guide had a length approximately equal to a quarter of a wavelength at the operating frequency of the magnetron.

10. The circuit of claim 1, further including a window sealing one of said wave guides to re-' tain the vacuum of said magnetron, said window being transparent to the energy propagated along said guides.

ALBERT M. CLOGSTON. ALEXANDER G. SMITH.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,247,077 Blewett et al June 24, 1941 2,283,935 King May 26, 1942 2,364,732 Ludi Dec. 12, 1944 2,372,193 Fisk Mar. 27, 1945 2,407,706 Shulman et al Sept. 17, 1946. 2,409,913 7 Tonks Oct. 22, 1946 2,489,131 Hegbar, Nov. 22, 1949 2,520,955 Okress et a1 Sept. 5, 1950 

